Kinetics and Thermodynamics: Analyzing Arguments Related to Reactions with Enolate Intermediates

This review extends on previously reported findings in which students were asked to construct Reaction Coordinate Diagrams (RCDs) de novo. Instead of asking students to construct RCDs, this study explores students’ understanding of kinetics and thermodynamics when provided with mechanisms for the Aldol and Claisen condensations. Data was collected using four cohorts to gain multiple perspectives on students’ reasoning and to gauge how instruction may impact reasoning. In Cohorts 1 and 2, a Qualtrics survey was administered to probe students’ conceptions of kinetics and thermodynamics for the Aldol condensation. Cohorts 1 and 2 differed concerning the scope of instruction about kinetics and thermodynamics related to Aldol condensation. With Cohort 3, interviews were conducted using the same survey questions administered with Cohorts 1 and 2 to extract further details regarding students’ reasoning relating to the intricacies of these mechanisms. Students in Cohort 3 did not receive targeted instruction. The study was expanded to consider the Claisen condensation, which forms an ester enolate intermediate, to further assess students’ reasoning and the impact of multiple layers of instruction related to energetics. Cohort 4 was tested on their knowledge of the energetics pertaining to Claisen condensation from an in-class evaluation; the students in this Cohort did receive explicit instruction about the relevant kinetic and thermodynamic facts of these reactions Stability, acidity, leaving group ability, and resonance were the common resources used by students in constructing arguments, which aligns with strategies used in the classroom. However, students often converged on the idea that kinetic and thermodynamic favorability are in alignment with one another, regardless of the reaction type. The results of the evaluation methods indicate that instruction about the energetics of the Aldol and Claisen condensations did not improve the student reasoning.

Duke Scholars

Author Charlie T. Cox Chemistry